The present invention relates generally to tools for tying wire. More particularly, this invention relates to portable, hand operated power tools for tying reinforcement rebar used in concrete construction.
As will be recognized by those skilled in the art, during concrete construction, arrays of reinforcement rods are erected within the forms so that when the concrete is poured, the resultant structure is strengthened by the "rebar." Typically intersecting sections of rebar are hand tied to each other with wire. Although it has been known in the prior art to provide various types of hand tools for tying rebar, numerous difficulties have existed in the past. One of the biggest problems is that prior art rebar tying tools tend to be cumbersome and heavy. To be effective on the job, an applicator tool must be relatively light weight and portable. However, the most important aspect is that of "reliability."
Prior art devices tend to be unreliable for several reasons. One reason is that most prior art devices are vulnerable to imperfections in the wire, caused by metal variances, kinks and the like. The relatively inexpensive and ductile wire used for tying rebar is difficult to reliably feed with mechanical devices. While the wire feed mechanism of such a device must be relatively powerful, the mechanism must not overpower the other working parts by unnecessarily forcing wire and jamming the mechanism. Through experimentation I have discovered that one secret of making a power rebar fastener system work properly is to provide a concentric interior construction in which the wire feeding and the jaw twisting section cooperate together about a central axis. Numerous other devices fail to appreciate this symmetry.
U.S. Pat. No. 4,362,192, issued Dec. 7, 1982 is typical of prior art power winding tools. This device is probably the closest known to me. It includes a rotating mandrel which functions in cooperation with a reciprocal jaw mechanism, but partially because the main jaws are both movable, tying problems are experienced. U.S. Pat. No. 3,391,715 issued Jul. 9, 1968, contemplates a jaw system which provides a looping mechanism, but the clamping solenoid system and the wire feed system do not feed wire through the construction herein disclosed. U.S. Pat. No. 3,169,559, Issued Feb. 16, 1965, discloses a system for tying rebar which is complicated by the fact that the applicator head includes rotating ears in the critical region for wire feeding. In other words the gear rotation and the wire feed occur transversely across an applicator region rather than at the output of a concentric system.
U.S. Pat. No. 4,834,148, Issued May 30, 1989, discloses a reinforcement binding machine having a pair of applicator jaws and a system for tying wire, but the jaws do not include a pair of fixed members with a captured looping jaw, and the wire feeding mechanism is not concentric with respect to the rotating barrel or mandrel. U.S. Pat. No. 4,953,598 discloses a hand-held power tool, but the applicator jaw is gear driven in a cumbersome fashion unlike our concentric layout. U.S. Pat. No. 4,498,506 discloses a wire system wherein the wire feeding mechanism is disposed in spaced relation with respect to the applicator head. The wire is fed through a cable so that the power wire feeding apparatus is unnecessarily separated from the critical applicator jaws. U.S. Pat. No. 4,685,493 issued Aug. 11, 1987, integrates the wire spool with the unit body, but does not include reciprocal jaws in the manner I have disclosed, nor does it include a concentric drive feed system which is responsible for reliability.
U.S. Pat. No. 4,177,842, issued Dec. 11, 1979, includes a feeding mechanism with a reciprocal jaw which attempts to provide looping, but the wire feed points are not controlled through the concentric arrangement I have proposed. The wire applicator head of Jones U.S. Pat. No. 3,026,915, Issued Mar. 27, 1962, discloses a rotating mandrel in which a pair of stops can catch wires fed on opposite sides of the mandrel, but lacks the concentric wire feeding system and jaw system herein disclosed.